[PATCH v3 2/3] s390x/pv: Introduce a s390_pv_check() helper for runtime

["Cédric Le Goater" <clg@kaod.org>]

From: Cédric Le Goater <clg@redhat.com>

If a secure kernel is started in a non-protected VM, the OS will hang
during boot without giving a proper error message to the user.

Perform the checks on Confidential Guest support at runtime with an
helper called from the service call switching the guest to protected
mode.

Signed-off-by: Cédric Le Goater <clg@redhat.com>
---

  In s390_pv_check(), drop the call to s390_pv_guest_check() since
  init time has already checked the same conditions. However, to
  report an error when the machine is not protected and the kernel
  secure, we still need s390_pv_check().

 include/hw/s390x/pv.h |  2 ++
 hw/s390x/pv.c         | 13 +++++++++++++
 target/s390x/diag.c   |  7 +++++++
 3 files changed, 22 insertions(+)

diff --git a/include/hw/s390x/pv.h b/include/hw/s390x/pv.h
index 9360aa1091..ca7dac2e20 100644
--- a/include/hw/s390x/pv.h
+++ b/include/hw/s390x/pv.h
@@ -55,6 +55,7 @@ int kvm_s390_dump_init(void);
 int kvm_s390_dump_cpu(S390CPU *cpu, void *buff);
 int kvm_s390_dump_mem_state(uint64_t addr, size_t len, void *dest);
 int kvm_s390_dump_completion_data(void *buff);
+bool s390_pv_check(Error **errp);
 #else /* CONFIG_KVM */
 static inline bool s390_is_pv(void) { return false; }
 static inline int s390_pv_query_info(void) { return 0; }
@@ -75,6 +76,7 @@ static inline int kvm_s390_dump_cpu(S390CPU *cpu, void *buff) { return 0; }
 static inline int kvm_s390_dump_mem_state(uint64_t addr, size_t len,
                                           void *dest) { return 0; }
 static inline int kvm_s390_dump_completion_data(void *buff) { return 0; }
+static inline bool s390_pv_check(Error **errp) { return false; }
 #endif /* CONFIG_KVM */
 
 int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp);
diff --git a/hw/s390x/pv.c b/hw/s390x/pv.c
index 8a1c71436b..8405e73a1b 100644
--- a/hw/s390x/pv.c
+++ b/hw/s390x/pv.c
@@ -306,6 +306,19 @@ int s390_pv_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
     return 0;
 }
 
+bool s390_pv_check(Error **errp)
+{
+    MachineState *ms = MACHINE(qdev_get_machine());
+
+    if (!ms->cgs) {
+        error_setg(errp, "Protected VM is started without Confidential"
+                   " Guest support");
+        return false;
+    }
+
+    return true;
+}
+
 OBJECT_DEFINE_TYPE_WITH_INTERFACES(S390PVGuest,
                                    s390_pv_guest,
                                    S390_PV_GUEST,
diff --git a/target/s390x/diag.c b/target/s390x/diag.c
index 76b01dcd68..9b16e25930 100644
--- a/target/s390x/diag.c
+++ b/target/s390x/diag.c
@@ -79,6 +79,7 @@ void handle_diag_308(CPUS390XState *env, uint64_t r1, uint64_t r3, uintptr_t ra)
     uint64_t addr =  env->regs[r1];
     uint64_t subcode = env->regs[r3];
     IplParameterBlock *iplb;
+    Error *local_err = NULL;
 
     if (env->psw.mask & PSW_MASK_PSTATE) {
         s390_program_interrupt(env, PGM_PRIVILEGED, ra);
@@ -176,6 +177,12 @@ out:
             return;
         }
 
+        if (!s390_pv_check(&local_err)) {
+            error_report_err(local_err);
+            env->regs[r1 + 1] = DIAG_308_RC_INVAL_FOR_PV;
+            return;
+        }
+
         s390_ipl_reset_request(cs, S390_RESET_PV);
         break;
     default:
-- 
2.39.0